Understanding PWM1 and PWM2 in Modern Electronic Circulators for Enhanced System Compatibility

In the world of electronic circulators, talking only about head, flow rate, and installation length is no longer enough. Today, compatibility with the system’s control logic is a decisive factor, especially when working with boilers, heat pumps, hybrid systems, solar installations, and advanced HVAC applications.

This is where PWM1 and PWM2 come into play: two external control modes that allow the generator or control unit to modulate the operation of the circulator more precisely than with a simple manual setting. Within the One Pump range, several models are specifically designed to handle these signals while also keeping traditional operating modes available, such as dP/V, dP/C, three fixed speeds and, in many cases, the Auto function. The OPE 6/8 IPWM1-2, GPA 11 H, GPA 25-12-180 / 32-12-180, GPA 17 HD, NEOS M 32-10-220F, and NEOS B series all offer compatibility with PWM1 and/or PWM2 together with internal electronic control modes.

Why PWM control has become central in modern circulators

The circulator is no longer a passive component. In modern machines, it must communicate with the system’s electronic board and adapt its performance to the actual demand of the installation. This is especially true for:

• condensing boilers;

• heat pumps;

• hybrid systems;

• solar systems;

• cooling and geothermal circuits;

• hydronic groups and commercial applications.

When a circulator is PWM-controlled, the machine does not simply power it: it actively controls it. In practical terms, the generator can modulate pump operation according to the required load, operating conditions, and the control logic of the system. One Pump offers several models specifically designed for this type of integration, while still maintaining alternative operating modes for cases in which external control is not used.

PWM1 and PWM2: what is the real difference?

It is worth being clear here. PWM1 and PWM2 are not interchangeable labels. In the One Pump catalogue, the application-based distinction is explicit: in some series, such as GPA 25-12-180 / 32-12-180 and NEOS M 32-10-220F, PWM1 is indicated as the control mode for boilers and heat pumps, while PWM2 is associated with solar applications. This is the technical point that really matters when selecting a replacement or planning a retrofit.

In other words:

• PWM1 is the control logic typically linked to boilers and heat pumps;

• PWM2 is the control logic typically used in solar applications.

The catalogue provides a detailed electrical overview of the protocols without going deeply into the electronic management of the signal itself. What can be said with certainty is that, within the One Pump range, the distinction between PWM1 and PWM2 is presented as a functional and application-based difference. For the installer, this matters far more than theory: if the machine controls in PWM1, a pump compatible with PWM1 is required; if the controller operates in PWM2, a pump able to recognize PWM2 is required.

The real advantage: a PWM pump that can also operate in traditional modes

The strength of the One Pump range is not just PWM compatibility. The real strength is its dual flexibility.

In fact, many models compatible with PWM1 and PWM2 can also operate using traditional internal control modes:

• 3 dP/V curves;

• 3 dP/C curves;

• 3 fixed speeds;

• Auto, where available.

This approach is very clear, for example, in the OPE 6 IPWM1-2 and OPE 8 IPWM1-2 series, which feature 9 curves, PWM1, PWM2, Auto, 3 dP/V, 3 dP/C, and 3 fixed speeds. The same pattern can be found in the GPA 11 H, GPA 25-12-180 / 32-12-180, GPA 17 HD, and NEOS M 32-10-220F families.

For those working in the replacement market, this means something very simple: the circulator is not tied to a single control logic. It can be installed as a PWM externally controlled pump, but it can also be used with traditional control settings when the signal is not present or not required. This is what makes the One Pump proposition particularly strong as a replacement solution.

OPE 6 IPWM1-2 and OPE 8 IPWM1-2: universal circulators for advanced residential applications

If one family really stands out as a versatile replacement option, it is the OPE 6 IPWM1-2 / OPE 8 IPWM1-2 series.

The catalogue describes it as a threaded series in DN 20/25/32 with 130 and 180 mm installation lengths, a head range of 6–8 meters, fluid temperature from -20 °C to +110 °C, compatibility with heating, air conditioning, and solar applications, and above all with:

• 9 curves;

• PWM1;

• PWM2;

• Auto;

• 3 dP/V;

• 3 dP/C;

• 3 fixed speeds;

• PWM1/A - PWM2/A signal cable.

Put bluntly: for many replacements on boilers, heat pumps, and mixed systems, these models are among the most interesting because they combine control compatibility with operating flexibility. They are not just PWM pumps. They are pumps that can also work well outside PWM mode.

GPA 11 H: higher head, dual PWM compatibility, and alternative control modes

When greater hydraulic performance is required, One Pump offers the GPA 11 H. The catalogue presents it as a series with up to 11 meters of head, fluid temperature from -10 °C to +110 °C, external control via PWM1/A and PWM2, as well as 9 curves, 3 dP/V, 3 dP/C, 3 fixed speeds, and Auto. The same family is also referenced for heat pump applications, with reference to EN 60335-2-40 relating to A3 refrigerant gases.

This is a series that makes sense when the old circulator requires a more powerful pump than the 6–8 meter range, while still needing compatibility with PWM logic and, alternatively, the option to operate in standard electronic mode.

GPA 25-12-180 and GPA 32-12-180: the application-based distinction between PWM1 and PWM2 is explicitly stated

In the GPA 25-12-180 / GPA 32-12-180 family, the catalogue is even more explicit. The control modes are listed as:

• 3 dP/V;

• 3 dP/C;

• 3 fixed speeds;

• Auto;

• PWM1 (Boiler - Heat pump);

• PWM2 (Solar).

Here, the difference between PWM1 and PWM2 is clearly stated at the application level. This is important because it makes this series particularly suitable as a replacement in systems where the external control mode is already defined by the generator. In addition, the same pump can also be used with traditional control settings, without forcing the system to operate exclusively in PWM. For this reason, the GPA 12 series is one of the most credible solutions when discussing complete replacement from a functional point of view.

GPA 17 HD: the solution for more demanding applications

Moving further up the range, the GPA 17 HD covers the high-head segment. The catalogue presents it with up to 17 meters of head, external control via PWM1/A and PWM2, 9 curves, 3 dP/V, 3 dP/C, 3 fixed speeds, and Auto. So here too the logic remains the same: the pump can be controlled by the machine’s electronics, while still retaining a full range of alternative operating modes.

For commercial systems, more structured heat pump applications, circuits with high pressure losses, or technically demanding retrofits, this is a sensible option. Not because it “does everything,” but because it addresses the key issue effectively: control compatibility, hydraulic performance, and alternative operating modes.

NEOS M 32-10-220F: compact flanged version with PWM1 and PWM2

Anyone moving from the threaded world to a flanged pump will find the NEOS M 32-10-220F in the catalogue, stated as available from July 2026. The product is described with:

• head up to 10 meters;

• 220 mm installation length;

• PWM1 (Boiler - Heat pump);

• PWM2 (Solar);

• 3 dP/V;

• 3 dP/C;

• 3 fixed speeds;

• Auto.

For compact retrofits and light commercial applications, it is an interesting solution because it brings the same design philosophy of the threaded models into a flanged configuration.

NEOS B: the widest and most flexible range

If the focus shifts to larger commercial systems, the NEOS B series is probably the most versatile offering in the One Pump range. The catalogue attributes the following features to it:

• 6 dP/V;

• 6 dP/C;

• 6 fixed speeds;

• Auto;

• Night shift;

• Wi-Fi;

• PWM1;

• PWM2;

• 0–10V with optional module.

The range goes from DN32 to DN80 and reaches up to 18 meters of maximum head. This makes NEOS B a very interesting platform not only for those looking for PWM1 or PWM2, but also for those who need to integrate the pump into more complex systems, where the control logic may vary from one installation to another.

0–10V module: when the pump needs to be integrated into systems using another type of control

Precision matters here. The accessories catalogue lists the “0–10V module for OPE, GPA, and NEOS B pumps,” code 4CI6050B. This means that, in some configurations, the OPE, GPA, and NEOS B series can also be integrated into systems where the available control signal is 0–10V.

The correct way to phrase it is this: One Pump provides a dedicated module for 0–10V integration on compatible series. This makes it possible to cover applications where the system does not natively operate in PWM but in 0–10V. Saying more than this, without a specific technical datasheet for the module, would be arbitrary. The essential point remains: the range does not stop at pure PWM, but can also enter analog control scenarios where provided by catalogue accessories.

Important: not the entire One Pump range is PWM-compatible

Not all One Pump circulators are compatible with PWM1 and PWM2.

For example, OPE 10 is a very interesting series in terms of construction and motor protection, but the catalogue table indicates PWM1/A and PWM2/A: NO. The pump operates with 3 dP/V, 3 dP/C, 3 fixed speeds, and Auto, but it should not be presented as a PWM pump.

Likewise, GPA 40-10F is presented as a pump with 27 control settings and a 0–10V input, not as a PWM pump. And the NEOS 1F/3F series is presented with 3 fixed curves and Auto dP/V, not as a PWM series. So the range is broad, but it has to be read carefully: PWM compatibility is there, and it is strong, but it does not apply across every single model.

One Pump PWM-compatible models to consider for replacement

If the goal is to identify the main One Pump models that can be proposed as functional replacements in externally controlled configurations, the clearest catalogue references are the following:

Models with PWM1 and PWM2

• OPE 20-6-130-IPWM 1-2

• OPE 25-6-130-IPWM 1-2

• OPE 25-6-180-IPWM 1-2

• OPE-32-6-180-IPWM 1-2

• OPE 20-8-130-IPWM 1-2

• OPE 25-8-130-IPWM 1-2

• OPE 25-8-180-IPWM 1-2

• OPE-32-8-180-IPWM 1-2

• GPA 25-11H-130

• GPA 25-11H-180

• GPA 32-11H-180

• GPA 25-12-180

• GPA 32-12-180

• GPA 25-17H-180

• GPA 32-17H-180

• NEOS M 32-10-220F

• NEOS B series from DN32 to DN80

Models with PWM1

• GPA 20-7.5-III-PRO-130

• GPA 25-7.5-III-PRO-130

• GPA 25-7.5-III-PRO-180

• GPA 32-7.5-III-PRO-180

Can One Pump be proposed as a complete replacement?

The serious answer is: yes, but only when the technical data are compatible.

From a functional standpoint, many One Pump series compatible with PWM1 and PWM2 can be proposed as complete replacements because they offer:

• compatibility with the external control signal;

• alternative operation in dP/V;

• alternative operation in dP/C;

• operation at three fixed speeds;

• Auto function, where available.

But “complete replacement” does not mean fitting any pump in place of any other. A replacement only makes sense if the following are compatible:

• connections;

• installation length;

• head;

• flow rate;

• power supply;

• fluid temperature;

• application field;

• control logic.

This conclusion is a technical deduction consistent with the catalogue characteristics: the range covers many configurations and offers broad control flexibility, but the selection still has to be made correctly. Put simply: anyone selling a replacement without checking the installation data is improvising.

Conclusion

The difference between PWM1 and PWM2 in the One Pump range should be understood in terms of what really matters in the field: compatibility with the machine’s control logic. PWM1 is associated with boilers and heat pumps; PWM2 is associated with solar applications. In many families, however, the real advantage is not only the external control input: it is the possibility of using the same circulator also in dP/V, dP/C, three fixed speeds, and Auto.

This is why One Pump is credible not only as original equipment, but also as a replacement and retrofit solution: it does not offer rigid pumps, but electronic circulators that adapt to different configurations. Where PWM1 or PWM2 is required, there are dedicated models. Where 0–10V is needed, there is a compatible module for GPA and NEOS B. Where external control is not available, traditional control modes remain. This is not a vague promise. It is a range designed intelligently.